1. Cross-Reference to Related, Copending Application
Related, copending application of particular interest to the instant application is U.S. Ser. No. 497,221, entitled "Data Transmission Apparatus", filed Mar. 22, 1990 and assigned to the same assignee of the instant application.
2. Field of the Invention
The present invention relates generally to interface apparatuses, and more specifically, to an interface apparatus controlling data transmission from a first apparatus to one or a plurality of second apparatuses.
3. Description of the Background Art
Handshaking type data transfer is conventionally known as data transfer in an information processing unit or the like. Data transfer from a first data transmission path to a second data transmission path by means of such handshaking type data transmission is, for example, conducted as follows.
Transmission signals are supplied from the first data transmission path to the second data transmission path, and transmission acknowledging signals are supplied from the second data transmission path to the first data transmission path. Data is supplied from the first data transmission path to the second data transmission path together with the transmission signals. The second transmission line, in response to the transmission signals, causes the transmission acknowledging signals to be inhibited in order to inhibit sending of further data for a fixed time period. After the elapse of the fixed time period, when the transmission acknowledging signals return to the authorized state data transmission from the first data transmission path to the second data transmission path is once again authorized. In this manner, the handshaking type data transmission is performed within an information processing unit or a plurality of information processing units.
When data transmission is conducted between a plurality of apparatuses, long signal lines for connecting these apparatuses to each other result in delay in signal transmission. As a result, some time period is required after data is supplied from the first apparatus to the second apparatus together with the transmission signals until the first apparatus receives a signal inhibiting sending of further data. Further data is therefore sent from the first apparatus to the second apparatus before reception of the data by the second apparatus is complete.
Furthermore, in data transmission from one apparatus to a plurality of apparatuses, if interconnection paths connected between these apparatuses are different in length every interconnection path will have a different signal delay time. Consequently, a delay circuit including a gate element or a delay circuit including a resistor or a capacitance element should be additionally provided in each path, in order to adjust timing skews of signals in the plurality of interconnection paths. The interconnection paths between the apparatuses usually change depending upon the placements of the apparatuses upon their actual installation, and, therefore, skew adjustment as described above will be necessary depending upon actual conditions for installing such a plurality of apparatuses.
Furthermore, when the transmission signals are transmitted in a form of pulse wave, depending upon the input load of the second apparatus which is subject to interface, a decrease in pulse width or a loss of pulse is effected due to lack of driving capability in the final stage of the first apparatus, or external noise comes in. This can cause the second apparatus to operate erroneously in data transmission.